Year	Number
1970	28.1412691712
1971	29.5483326298
1972	30.9553960884
1973	32.3624595469
1974	33.7695230055
1975	35.176586464
1976	36.5836499226
1977	37.9907133812
1978	39.3977768397
1979	40.8048402983
1980	42.2119037569
1981	43.6189672154
1982	45.026030674
1983	46.4330941325
1984	47.8401575911
1985	49.2472210497
1986	52.0613479668
1987	54.8754748839
1988	57.689601801
1989	60.5037287182
1990	62.4173350218
1991	64.1017178966
1992	65.7861007713
1993	67.4704836461
1994	69.1548665208
1995	70.8392493956
1996	72.5236322704
1997	74.2080151451
1998	75.8923980199
1999	77.5767808946
2000	79.2611637694
2001	81.7105201445
2002	85.0373724582
2003	87.5228008238
2004	90.0082291893
2005	92.4936575549
2006	94.9790859204
2007	97.464514286
2008	99.9499426515
2009	102.4353710171
2010	104.9207993826
2011	107.4062277481
2012	109.7509497678
2013	115.1634538718
2014	120.5759579757
2015	125.9884620796
2016	129.8719572253
2017	137.9203602082
2018	137.9203602082
2019	137.9203602082
2020	137.9203602082